| 1. |
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| 2. |
- Donchev, V., et al.
(författare)
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Enhancement of the photoluminescence intensity of a single InAs/GaAs quantum dot by separate generation of electrons and holes
- 2006
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Ingår i: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 48:10, s. 1993-1999
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that the microphotoluminescence (µPL) spectrum of a single InAs/GaAs self-assembled quantum dot (QD) undergoes considerable changes when the primary laser excitation is complemented with an additional infrared laser. The primary laser, tuned slightly below the GaAs band gap, provides electron-hole pairs in the wetting layer (WL), as well as excess free electrons from ionized shallow acceptors in the GaAs barriers. An additional IR laser with a fixed energy well below the QD ground state transition generates excess free holes from deep levels in GaAs. The excess electron and hole will experience diffusion separately, due to the time separation between the two events of their generation, to eventually become captured into the QD. Although the generation rates of excess carries are much lower than that of the electron-hole pair generation in the WL, they considerably influence the QD emission at low temperatures. The integrated PL intensity increases by several times as compared to single-laser excitation, and the QD exciton spectrum is redistributed in favor of a more neutral charge configuration. The dependence of the observed phenomenon on the powers of the two lasers and the temperature has been studied and is consistent with the model proposed. The concept of dual excitation could be successfully applied to different low-dimensional semiconductor structures in order to manipulate their charge state and emission intensity. © Nauka/Interperiodica 2006.
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| 3. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Carrier diffusion in the barrier enabling formation of charged excitons in InAs/GaAs quantum dots
- 2001
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Ingår i: XXX International School on the Physics of Semiconducting Compounds,2001. - : Polish Academy of Sciences, Institute of Physics. ; , s. 387-395
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Konferensbidrag (refereegranskat)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the experimental conditions, such as excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusion of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots. This is proposed as a new tool to populate quantum dots with extra electrons in order to study phenomena involving charged excitons.
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| 4. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Effective tuning of the charge-state of single In(Ga)As/GaAs quantum dots by below barrier band gap excitation
- 2003
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 532-535, s. 843-847
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Tidskriftsartikel (refereegranskat)abstract
- The existence of a well-defined threshold energy, crucial for the charging of quantum dots (QDs), positioned between the barrier band gap and the wetting layer ground state is demonstrated. Optical excitation with energies above this threshold populates the QDs with extra electrons. The origin of the threshold is discussed in terms of acceptors in the GaAs barrier. ⌐ 2003 Elsevier Science B.V. All rights reserved.
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| 5. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Optical charging of self-assembled InAs/GaAs quantum dots
- 2002
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Ingår i: Physica scripta. T. - 0281-1847. ; 101, s. 140-142
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the experimental conditions, such as excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusion of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots. This is proposed as an effective tool to populate single quantum dots with extra electrons, by purely optical means, in order to study phenomena involving charged excitons.
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| 6. |
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| 7. |
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| 8. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Temperature influence on optical charging of self-assembled InAs/GaAs semiconductor quantum dots
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:19, s. 2952-2954
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled InAs/GaAs quantum dots are very sensitive to excitation energy and crystal temperature. This is qualitatively explained in terms of the effective diffusivity of photogenerated particles, which affects the capture probability of the quantum dot. As a consequence, this opens the possibility of controlling the average number of excess electrons in the quantum dot by optical means. This technique may be used as a simple tool to create and study charged exciton complexes without any specially fabricated samples. ⌐ 2001 American Institute of Physics.
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| 9. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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The influence of carrier diffusion on the formation of charged excitons in InAs/GaAs quantum dots
- 2002
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 101-104
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusivity of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots (QDs). This is proposed as an effective tool to populate quantum dots with extra electrons in order to study phenomena involving charged excitons. ⌐ 2002 Elsevier Science B.V. All rights reserved.
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| 10. |
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| 11. |
- Moskalenko, Evgenii, 2000-, et al.
(författare)
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Acceptor-induced threshold energy for the optical charging of InAs single quantum dots
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:19, s. 1953321-19533211
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Tidskriftsartikel (refereegranskat)abstract
- We study the photoluminescence of single InAs/GaAs self-assembled quantum dots for a range of excitation powers, excitation energies and sample temperatures 4 K30 K), this effect vanishes due to the essential decrease of the steady-state free electron concentration in the GaAs barrier as a result of thermally excited free holes appearing in the GaAs barrier valence band which provides an effective recombination channel for the free electrons. These experimental observations could be used as an effective tool to create and study charged excitons in quantum dots.
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| 12. |
- Moskalenko, Evgenii, 2000-, et al.
(författare)
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Effect of an additional infrared excitation on the luminescence efficiency of a single InAs/GaAs quantum dot
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:15, s. 1553171-15531714
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Tidskriftsartikel (refereegranskat)abstract
- Microphotoluminescence (PL) spectra of a single InAs/GaAs self-assembled quantum dot (QD) are studied under the main excitation of electron-hole pairs in the wetting layer (WL) and an additional infrared (IR) laser illumination. It is demonstrated that the IR laser with fixed photon energy well below the QD ground state induces striking changes in the spectra for a range of excitation energies and powers of the two lasers. For the main excitation above a threshold energy, defined as the onset of transitions between shallow acceptors and the conduction band in GaAs, the addition of the IR laser will induce a considerable increase in the QD emission intensity. This is explained in terms of additional generation of extra electrons and holes into the QD by the two lasers. For excitation below the threshold energy, the carrier capture efficiency from the WL into the QD is suggested to be essentially determined by the internal electric-field-driven carrier transport in the plane of the WL. The extra holes, generated in the GaAs by the IR laser, are supposed to effectively screen the built-in field, which results in a considerable reduction of the carrier collection efficiency into the QD and, consequently, a decrease of the QD PL intensity. A model is presented which allows estimating the magnitude of the built-in field as well as the dependence of the observed increase of the QD PL intensity on the powers of the two lasers. The use of an additional IR laser is considered to be helpful to effectively manipulate the emission efficiency of the quantum dot, which could be used in practice in quantum-dot-based optical switches.
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| 13. |
- Moskalenko, Evgenii, 2000-, et al.
(författare)
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Formation of the charged exciton complexes in self-assembled InAs single quantum dots
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:11, s. 6787-6793
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Tidskriftsartikel (refereegranskat)abstract
- The low-temperature photoluminescence (PL) of the self-assembled InAs single quantum dots (QD) was studied using micro-PL setup. It was demonstrated that two emission lines down shifted in energy with respect to the ground state exciton PL line appeared in the PL spectrum. The PL intensity of these lines showed a periodic behavior with the excitation energy.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Paskov, Plamen, et al.
(författare)
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Auger processes in InAs self-assembled quantum dots
- 2000
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 6:1, s. 440-443
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Tidskriftsartikel (refereegranskat)abstract
- An experimental evidence of Auger-like excitation processes in InAs/GaAs quantum dots is demonstrated. Photoluminescence spectra of resonantly excited dots exhibit a rich satellite structure below the ground-state emission band. The energy position and the intensity distribution of the satellites are analyzed and an interpretation of the satellites as due to shake-up processes of the interacting careers in the higher quantum dot states is suggested.
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| 19. |
- Paskov, Plamen, et al.
(författare)
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Magnetoluminescence of highly excited InAs/GaAs self-assembled quantum dots
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:11, s. 7344-7349
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Tidskriftsartikel (refereegranskat)abstract
- We present magnetoluminescence measurements of InAs/GaAs self-assembled quantum dots (QD's) at different excitation intensities. By applying high excitation intensities, the magnetic field evolution of the excited-state emission of QD's is revealed. A splitting of the states with a nonzero magnetic momentum is observed and the in-plane reduced electron-hole mass is determined. The experimental value is found to be in a good agreement with the theoretical predictions based on the eight-band k·p model including both strain effect and band nonparabolicity. The density dependence of the diamagnetic shift of the ground-state emission is also studied providing evidence for screening of the Coulomb interaction in QD's.
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| 20. |
- Paskov, Plamen, 1959-, et al.
(författare)
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Optical up-conversion processes in InAs quantum dots
- 2000
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Ingår i: the 25th International Conference on the Physics of Semiconductors ICPS-25,2000. ; , s. 2080-2083
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Konferensbidrag (refereegranskat)abstract
- Up-converted photoluminescence (UPL) in InAs/GaAs self-assembled quantum dots (QDs) is reported. With a resonant excitation of QDs we observe an efficient emission from the GaAs barrier. The excitation spectrum of the UPL shows that the signal disappears if the excitation energy is tuned below the absorption band of the QDs. The intensity of UPL exhibits an almost quadratic dependence on the excitation intensity. The observed effect is explained by a two-step two-photon absorption process involving quantum dot states as intermediate states.
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| 21. |
- Paskov, Plamen, 1959-, et al.
(författare)
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Optical up-conversion processes in InAs quantum dots
- 2001
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Ingår i: Japanese Journal of Applied Physics. - 0021-4922 .- 1347-4065. ; 40:3 B, s. 2080-2083
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Tidskriftsartikel (refereegranskat)abstract
- Up-converted photoluminescence (UPL) in InAs/GaAs self-assembled quantum dots (QDs) is reported. With a resonant excitation of QDs we observe an efficient emission from the GaAs barrier. The excitation spectrum of the UPL shows that the signal disappears if the excitation energy is tuned below the absorption band of the QDs. The intensity of UPL exhibits an almost quadratic dependence on the excitation intensity. The observed effect is explained by a two-step two-photon absorption process involving quantum dot states as intermediate states. ⌐ 2001 The Japan Society of Applied Physics.
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| 22. |
- Paskov, Plamen, 1959-, et al.
(författare)
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Photoluminescence up-conversion in InAs/GaAs self-assembled quantum dots
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:6, s. 812-814
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Tidskriftsartikel (refereegranskat)abstract
- We report up-converted photoluminescence in a structure with InAs quantum dots embedded in GaAs. An efficient emission from the GaAs barrier is observed with resonant excitation of both the dots and the wetting layer. The intensity of the up-converted luminescence is found to increase superlinearly with the excitation density. The results suggest that the observed effect is due to a two-step two-photon absorption process involving quantum dot states. ⌐ 2000 American Institute of Physics.
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| 23. |
- Solomonidou, A., et al.
(författare)
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Spectral and emissivity analysis of the raised ramparts around Titan's northern lakes
- 2020
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Ingår i: Icarus. - : Academic Press. - 0019-1035 .- 1090-2643. ; 344
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Tidskriftsartikel (refereegranskat)abstract
- Some of Titan's small northern hemisphere lakes show raised rampart features (which are distinct from raised rims), and appear as SAR-bright mound-like annuli extending away from the lake for up to tens of kilometers from the shoreline. We investigate the infrared and microwave characteristics of these features using Cassini Visual and Infrared Mapping Spectrometer (VIMS) and RADAR data. A spectral comparative analysis is performed among the lakes, their ramparts, and the surrounding regions. We overcome the profound difference in spatial resolution between VIMS and SAR data by using a method that provides overlays between the spectral images and SAR, thus enabling the correct selection of VIMS pixels. The surface properties of the selected areas are obtained using a radiative transfer analysis on the selected VIMS pixels, in addition to emissivity obtained from the RADAR in radiometry mode. Analysis of these combined and co-registered data provides constraints for the formation mechanism(s) of raised ramparts. The results show that the emissivity of the raised ramparts is close to that of Titan's labyrinthic terrains and to that of empty lake floors in the northern polar regions. This is confirmed by the VIMS analysis that also shows that the infrared spectral response of the raised ramparts is very similar to that of some empty lake floors. This suggests that both areas are made from or are covered by a similar material. In addition, two out of the eight lakes with raised ramparts show spectral differences at three specific wavelengths, 1.6, 2.0, and 5.0 mu m, between the ramparts and the surrounding terrain. We hypothesize that this could be due to some component, or mixture of components in the ramparts that is less absorbent at these specific wavelengths, or it could be an effect of different grain sizes. These observations provide first insights into the possible mechanisms leading to the formation of the raised ramparts that are discussed here.
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